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The parallel surface thrust bearing has been studied both theoretically and experimentally. The general equations governing the laminar flow of a Newtonian fluid are presented and suitably reduced to describe the flow of lubricant through a plain collar bearing. A computer solution of the resulting equations has been obtained in which the variations, of density and viscosity with temperature are accommodated and the circumferential leakage of oil from the bearing is recognised. The resulting performance curves indicate that useful load carrying capacities, produced by a 'thermal wedge' effect, are possible with parallel surface thrust bearings. A series of tests was carried out on a three inch diameter bearing operating at speeds ranging from 15,000 to 19,000 r.p.m. The results confirm that hydrodynamic lubrication may be achieved with a parallel surface thrust bearing. The experimental values obtained for the load carrying capacity and the coefficient of friction were both less than the theoretical predictions. The discrepancies appear to be caused, for the most part, by an increase in the oil temperature resulting from entrainment of the lubricant in the bearing. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

The static friction of steel under boundary lubricated conditions was investigated both experimentally and theoretically. The theoretical model was developed using the assumption that during the application of a tangential load to a friction couple, the real area of contact grows in a viscoelastic manner until a critical shear stress is reached. Using this model, it was possible to distinguish the effect of static and dynamic contact time on area growth and thus to show why the traditional "time dependence of static friction" theories have limited validity. The model predicts that µs, the static friction coefficient, is a function of the rate parameter θ, and that a relaxation time can be assigned to a given interface. Subsequent experimental work using steel surfaces in vacuum as well as steel surfaces lubricated by various surface films showed that surface conditions play a large role in determining the exact µs - θ relationship for a given friction couple. Over the range of θ investigated the static friction coefficient of steel is constant if certain surface films are present; for other films the static friction coefficient vs θ curve shows an upper and lower asymptote. In the latter case a relaxation time was assigned to each boundary lubricant. For given asymptotes these relaxation times can be used to predict whether the film will be a useful lubricant at a particular θ. A subsequent investigation showed that the relaxation times are strongly affected by temperature. Since raising the substratum temperature results in smaller relaxation times, it is obvious that a particular lubricant may become ineffective as the substratum temperature changes. Both the experimental and theoretical work clearly demonstrate that the static friction of steel can be significantly modified by the application of appropriate boundary lubricants. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

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M.Tech. (Mechanical Engineering) / This study investigated process development of recovering base oils from waste lithium based lubricating grease using a novel combination of thermal degradation in an aqueous caustic solution and solvent extraction. Lubricating greases consist of a thickening agent dispersed in mineral or synthetic oil, forming a colloidal suspension [1]. Large and increasing volumes of used lubricating oil and grease are produced each year and are considered hazardous wastes. During operation, grease suffers mechanical and thermal degradation [2]. Subsequently, it is regarded as waste and it must be disposed. The waste oil should be collected and recycled not only to prevent the environmental pollution but also to preserve natural resources. Solvent extraction is the preferred method to recycle waste lubricants as it is cost-effective and requires no further purification of the product [3]. The influence of extraction temperature, agitation strength, extraction time, degrading agent concentration, degrading agent-to-grease and solvent-to-sludge mixing ratios on base oil recovery from waste lubricating grease was investigated. This study further optimised the process by studying the influence of various degrading agents (LiOH, NaOH and KOH) and solvents (n-hexane, toluene, heptane, butane, hexanol and acetone) on oil recovery. Oil recovery was enhanced by increase in both extraction temperature, time and agitation speed. The optimum extraction time was found to be 12 minutes. KOH was found to be the optimum degrading agent compared to LiOH and NaOH. Oil recovery also increased from 8.04% to 36.87% with increase in KOH m/m from 5% to 30%. The recovery also increased with an increase of solvent-to-sludge ratio up to 1:6. n-Hexane gave the highest recovery of 74.39% while acetone gave the lowest of 7.43%. A solvent recovery of 82.6% to 88% was obtained through fractional distillation. The study also investigated the differences between virgin and recycled oil using atomic absorption (AA), inductively coupled plasma (ICP) and Fourier transform infrared radiation (FTIR). Rheological studies of waste grease derived oil (WGDO) were also performed. ICP results showed traces of some elements such as Fe, Cu, Si, Ni and Al at a concentration of less than 0.9 mg/L. Oxidation was observed to occur at a band length of 1716 cm-1 while additives were identified at 1670 - 1725 cm-1. The oil viscosity slightly increased with increasing shear rate at temperatures between 60°C and 120°C. The shear rate was varied from 200 to 1000 1/s, with a viscosity convergence at 100°C. A financial economic model was applied to investigate the feasibility of the recycling technology. For 800 kg/day treatment plant, an investment of R 6,031,304.27 is required with a potential return on investment of 40%. Recovery was found to be favourable option compared to landfilling as it offers both economic and environmental benefits.

Thesis (Ph. D.)--University of North Texas, Dec., 2008. / Title from title page display. Includes bibliographical references.

Thesis (M.S.)--University of Wisconsin--Madison, 1965. / eContent provider-neutral record in process. Description based on print version record. Bibliography: l. 64-66.

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

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